Compact Discs have supplanted cassette tapes and all earlier technologies as the best way to record and play music.  Here’s how they work.

The principle material in a CD is a single disc of polycarbonate plastic.  During production, the plastic is imprinted with a series of microscopic indentations arranged in a single spiral from the outer edge of the circle to the center.   

The spiral is extremely long and thin.  If you were to take it off the disc and stretch it straight, it would be over three and a half miles in length. This is the music, converted to binary code and embedded in digital format on the surface of the CD.  

After the information is embedded in the plastic, a layer of reflective aluminum is added.  Afterward, an acrylic layer is sprayed on to protect the CD from the wear and tear of handling.

To read the information on the CD, a laser beam is focused on the line of binary information (the “bumps”).   The reflective aluminum layer causes the laser beam to reflect back onto a sensor, and the varying sizes of the bumps cause the reflections to change slightly as the disc spins.  

These varying signals of light are interpreted by an analog converter into an analog signal.  The analog signal is then amplified in your speakers, and comes out as music to your ears.

One drawback of modern CD’s is the rewriting option.  Customers love making their own mix CD’s, and they can do it by using either a CD-R or a CD-RW.  CD-R’s are cheap and compatible with almost every CD player, but they can only be recorded once.  CD-RW’s can be erased and re-recorded.  They are more expensive, however, and don’t work in all players.